Virtual image display device

ABSTRACT

A half mirror layer has an angle dependency in which when an angle of incidence becomes larger than the angle of incidence range of image light, reflectance increases, such that it is possible to prevent unintended light, which is emitted to a light transmitting member from a light guiding member and is reflected inside a light transmitting member, from being returned to a light emission portion of the light guiding member after passing through the half mirror layer as a reflective film at a relatively large angle of incidence. Therefore, it is possible to prevent the image light passed through the light transmitting member from becoming ghost light while mitigating the demand for increasing processing accuracy of the light transmitting member, and bonding accuracy between the light guiding member and the light transmitting member, to provide a high quality virtual image displayed by a virtual image display device.

This is a divisional application of application Ser. No. 13/968,912filed Aug. 16, 2013, which in turn is a divisional application ofApplication No. 131361,249 filed Jan. 30, 2012, which claims priority toJP 2011-022443 filed in Japan on Feb. 4, 2011. The disclosure of theprior applications is hereby incorporated by reference herein in itsentirety.

BACKGROUND

1. Technical Field

The present invention relates to a virtual image display device such asa head-mounted display that is used by being mounted on the head.

2. Related Art

In recent years, as a virtual image display device that allows a virtualimage to be formed and to be observed similarly to the head-mounteddisplay, various virtual image display devices of a type in which imagelight from a display element is guided to a pupil of an observer by alight guiding plate have been suggested.

In this virtual image display device, the image light and external lightoverlap with each other, such that a see-through optical system has beensuggested (refer to JP-A-2006-3879 and JP-A-2010-224473).

However, in the device disclosed in JP-A-2006-3879 or the like, thesee-through is realized by a pupil division method that uses a lightguiding optical system in which an emission opening is smaller than apupil size, such that it is difficult to make a display size of thevirtual image large. In addition, the light guiding optical system thatis smaller than the size of the pupil is used, such that it is difficultto make an effective pupil diameter (a lighting diameter that allows thevirtual image to be taken in, and is called an Eyring diameter) large soas to correspond to an individual pupil width in human beings. Inaddition, the emission opening or a casing of the light guiding opticalsystem is physically disposed in the vicinity of the pupil, such that ablind spot is generated, and therefore it is not necessarily a perfectsee-through.

In addition, as an optical system for the head-mounted display, anoptical system including a light guiding pipe that allows a plurality oflight modes in which the light guiding angles are different from eachother to progress (refer to JP-A-2008-535001) is disclosed. In thisoptical system, it may be considered that a third optical surface at anemission side is set as a half mirror, and light that is transmittedthrough the third optical surface is made to go straight to realize asee-through type display device.

However, in the optical system disclosed in JP-A-2008-535001, a liquidcrystal panel is illuminated with collimated light in which a differentangle of incidence is set for each of the optical modes on theassumption that a phase of each of the plurality of optical modes ismisaligned. In addition, display content is changed by each opticalmode, and a display of each optical mode is sequentially performed, andthereby an image of each optical mode is connected to obtain an entireimage. In this case, a center image and left and right images, whichmake up the entire image, are necessary to be displayed while these arechanged at a time difference by one liquid crystal panel, such that avirtual image display device becomes complex and an observed imagebecomes dark.

Separately from this configuration, it may be considered that a virtualimage display device that allows a virtual image to be observed in anoverlapped manner with external light by a light guiding member providedwith a light emitting portion to cover the front of an eye, in which itis not necessary to connect an image at a time difference. However, itis difficult to display a large image, and in a case where a member suchas a see-through prism is connected to the light guiding member, ghostlight is generated due to this member and therefore the ghost lighteasily reaches an eye.

SUMMARY

An advantage of some aspects of the invention is to provide a virtualimage display device that enables a see-through observation and candisplay a virtual image of a high quality by suppressing observation ofghost light.

An aspect of the invention is directed to a virtual image display deviceincluding (a) a light guiding member that includes a light guidingportion, a light incidence portion that allows image light to beincident to the light guiding portion, and a light emission portion thatemits the image light guided by the light guiding portion to theoutside, and that makes the image light visible through the lightemission portion; and (b) a light transmitting member that makes up asee-through portion that allows external light to be observed through acombination with the light guiding member, in which (c) a reflectivefilm having a light transmitting property and an angle dependency inwhich when an angle of incidence becomes larger than the angle ofincidence range of the image light, reflectance increases is providedbetween the light emission portion and the light transmitting member.

According to this virtual image display device, the reflective filmprovided between the light emission portion and the light transmittingmember has an angle dependency in which when the angle of incidencebecomes larger than the angle of incidence range of the image light, thereflectance increases, such that it is possible to prevent unintendedlight, which is emitted to the light transmitting member from the lightguiding member and is reflected inside the light transmitting member,from being returned to the light emission portion of the light guidingmember after passing through the reflective film at a relatively largeangle of incidence. Therefore, it is possible to prevent the image lightpassed through the light transmitting member from becoming ghost light,and thereby it is possible to make a virtual image displayed by thevirtual image display device have a high quality.

In a specific aspect of the invention, the virtual image display devicemay be configured such that the reflective film has a characteristic inwhich the reflectance varies in a stepwise fashion with a predeterminedlower limit angle given as a boundary, and reflects light having anangle of incidence larger than the lower limit angle and uniformlytransmits light having an angle of incidence smaller than the lowerlimit angle. In this case, it is possible to reliably see throughexternal light in which an angle of incidence is smaller than the lowerlimit angle, and thereby it is possible to reliably exclude unnecessarylight that is incident to the reflective film from a rear side at anangle larger than the lower limit angle.

In another aspect of the invention, the virtual image display device maybe configured such that the reflective film is formed by laminatingplural kinds of films. Therefore, it is easy to have a desired angledependency that is difficult to be realized in a single layer, withrespect to the reflectance of a reflective film.

In still another aspect of the invention, the virtual image displaydevice may be configured such that the reflective film has a structurein which a metallic reflective film and a dielectric multi-layer filmare laminated. In this case, it is possible to suitably block the ghostlight in which the angle of incidence is relatively large whilepreventing disturbance or useless attenuation in image light to bereflected.

In yet another aspect of the invention, the virtual image display devicemay be configured such that the reflective film includes asemi-transmissive reflective film including an Ag film whosetransmittance is adjusted as the metallic reflective film. The Ag filmserves as a half mirror in which absorption is small and efficiency ishigh. In addition, in the Ag film, sensitivity in the transmittance withrespect to increase or decrease in a film thickness is lower than a caseof Al film or the like, and it is easy to perform an adjustment of thereflectance or the transmittance.

In still yet another aspect of the invention, the virtual image displaydevice may be configured such that the reflectance of the reflectivefilm is 10% to 50% with respect to the image light. In this case, itbecomes easy to observe external light, that is, an external image via asee-through.

In further another aspect of the invention, the virtual image displaydevice may be configured such that the light guiding portion has a firstreflective surface and a second reflective surface that are disposed inparallel with each other and allow light to be guided through a totalreflection, the light incidence portion has a third reflective surfacethat makes a predetermined angle with respect to the first reflectivesurface, the light emission portion has a fourth reflective surface thatmakes a predetermined angle with respect to the first reflectivesurface, the light transmitting member has a wedge-shaped member havinga light transmitting surface bonded to the fourth reflective surface ofthe light emission portion through the reflective film, and thereflective film is disposed between the fourth reflective surface andthe light transmitting surface. According to this virtual image displaydevice, image light reflected by the third reflective surface of thelight incidence portion is propagated while being totally reflected bythe first and second reflective surfaces of the light guiding portion,is reflected by the fourth reflective surface of the light emissionportion, and is incident to observer's eye as a virtual image. In thiscase, it is possible to form the light guiding member as a member havingan external form of a polygonal block shape, such that it is easy toassemble the light guiding member into the virtual image display device,and the virtual image may be observed with high accuracy. In addition,in a see-through observation over the half mirror of the fourthreflective surface, distortion may be small due to the lighttransmitting portion.

In still further another aspect of the invention, the virtual imagedisplay device may be configured such that the light guiding portion hasan end surface that blocks the ghost light at a position at least one ofportions between the first reflective surface and the fourth reflectivesurface, and between the first reflective surface and the thirdreflective surface. Therefore, it is possible to further suppress theghost light.

In yet further another aspect of the invention, the virtual imagedisplay device may be configured such that the light transmitting memberhas a first surface and a second surface that are disposed in parallelwith the first reflective surface and the second reflective surface,respectively. Therefore, in the see-through observation via the lighttransmitting member, distortion does not occur and flatness becomeshigh.

In still yet further another aspect of the invention, the virtual imagedisplay device may be configured to further include an image displaydevice that forms image light, and a projective optical system thatmakes the image light emitted from the image display device be incident.The number of times of reflection of first image light, which is emittedfrom a first partial region in the image display device, in the lightguiding portion, and the number of times of reflection of second imagelight, which is emitted from a second partial region different from thefirst partial region in regard to a confinement direction in which areturn of the optical path due to reflection occurs at the time oflight-guiding, in the light guiding portion may be different from eachother. In this case, image light beams in which the number of times ofreflection is different are used, such that it is possible to make anangle of emission of the image light emitted from the light emissionportion have a wide angle width. That is, it is possible to take inimage light from a different display position in an image display deviceat a relatively wide viewing angle, such that it is possible to secure alarge display size in a virtual image that is observed over the lightemission portion. In this way, it is configured to have a structure inwhich image light beams in which the number of times of reflection isdifferent are taken out, such that it is possible to make the lightemission portion large so as to cover a pupil without making the lightguiding portion too much thicker, and thereby preferable see-throughobservation may be realized.

In a further aspect of the invention, the virtual image display devicemay be configured such that the confinement direction is a directionthat is parallel with a cross-section including a first optical axis inwhich the first image light and the second image light pass through theprojective optical system and a normal line of the third reflectivesurface. In the image light beams from different positions in relationto the cross-sectional direction, angles of emission, that is, angles ofincidence to the light incidence portion are made to be different fromeach other, such that it is possible to make the number of times ofreflection inside the light guiding portion different.

In a still further aspect of the invention, the virtual image displaydevice may be configured such that each of the light guiding member andthe light transmitting member is integrally molded independently throughan injection molding. In this case, it is possible to produce the lightguiding member and the light transmitting member with high accuracyusing an injection molding technique.

In a yet further aspect of the invention, the virtual image displaydevice may be configured such that the light guiding member and thelight transmitting member are molded from a thermal polymerization typeresin material, respectively. In this case, it is possible to increaseweight reduction or safety due to the resin, and thereby a stable andhighly accurate molding due to thermosetting may be realized.

A still yet further aspect of the invention is directed to a virtualimage display device including a light guiding member that includes alight guiding portion, a light incidence portion that allows image lightto be incident to the light guiding portion, and a light emissionportion that emits the image light guided by the light guiding portionto the outside, and that makes the image light visible through the lightemission portion; and a light transmitting member that makes up asee-through portion that allows external light to be observed through acombination with the light guiding member, in which a semi-transmissivereflective surface, which prevents light incident to the lighttransmitting member from the light emission portion of the light guidingmember from being incident again to the light guiding member side, isprovided.

According to this virtual image display device, the semi-transmissivereflective surface prevents light incident to the light transmittingmember from the light emission portion of the light guiding member frombeing incident again to the light guiding member side, such that it ispossible to prevent the image light passed through the lighttransmitting member from becoming ghost light, and thereby it ispossible to make the virtual image displayed by the virtual imagedisplay device have a high quality.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numbers reference like elements.

FIG. 1 is a perspective view illustrating a virtual image display deviceof an embodiment;

FIG. 2A is a plan view of a main body portion of a first display devicemaking up the virtual image display device, and FIG. 2B is a frontelevation view of the main body portion;

FIG. 3A is a diagram illustrating a structure of a third reflectivesurface in a light incidence portion of a light guiding member, FIG. 3Bis a diagram illustrating a structure of a first reflective surface in alight guiding portion of the light guiding member, FIG. 3C is a diagramillustrating a structure of a second reflective surface in the lightguiding portion of the light guiding member, and FIG. 3D is a diagramillustrating a structure of a fourth reflective surface in a lightemission portion of the light guiding member;

FIG. 4 is a graph illustrating a reflectance characteristic of a halfmirror layer;

FIG. 5 is a graph illustrating a wavelength dependency of thereflectance at a different angle of incidence;

FIG. 6A is a conception diagram in which an optical path in relation toa first vertical direction is developed, and FIG. 6B is a conceptiondiagram in which an optical path in relation to a second horizontaldirection is developed;

FIG. 7 is a plan view specifically illustrating an optical path in anoptical system of a virtual display device;

FIG. 8A is a diagram illustrating a display surface of a liquid crystaldisplay device, FIG. 8B is a diagram illustrating a conception of avirtual image of the liquid crystal display device, which is viewed byan observer, and FIGS. 8C and 8D are diagrams illustrating two partialimages making up the virtual image;

FIG. 9 is an enlarged diagram illustrating a processing of ghost lightin a light guiding device;

FIG. 10A is a diagram illustrating a light guiding state of image lightin a modification, and FIG. 10B is a diagram illustrating a conceptionof a virtual image of a liquid crystal display device in themodification;

FIG. 11 is a diagram illustrating the reason why an end surface formedby removing a corner is provided to the light guiding member; and

FIG. 12 is a diagram illustrating a modification of the light guidingmember shown in FIG. 2A or the like.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, a virtual image display device related to one embodiment ofthe invention will be described in detail with reference to theaccompanying drawings.

A. External Appearance of Virtual Image Display Device

A virtual image display device 100 of an embodiment illustrated in FIG.1 is a head-mounted display having the same external appearance aseyeglasses, and allows an observer wearing this virtual image displaydevice 100 to perceive image light via a virtual image and allows theobserver to observe an external image via a see-through. The virtualimage display device 100 includes an optical panel 110 that covers thefront of the observer's eyes, a frame 121 that maintains the opticalpanel 110, and first and second driving portions 131 and 132 that areprovided at a portion ranging from arm to temple of the frame 121. Here,the optical panel 110 includes a first panel portion 111 and a secondpanel portion 112, and the both panel portions 111 and 112 are formed ofa plate-shaped part and are integrally connected at the center of theoptical panel 110. A first display device 100A including the first panelportion 111 and the first driving portion 131 at the left-side in thedrawing is a portion that forms a left-eye virtual image, and alsofunctions independently as a virtual image display device. In addition,a second display device 100B including the second panel portion 112 andthe second driving portion 132 at the right-side in the drawing is aportion that forms a right-eye virtual image, and also functionsindependently as a virtual image display device.

B. Structure of Display Device

As shown in FIG. 2A or the like, the first display device 100A includesan image forming device 10 and a light guiding device 20. Here, theimage forming device 10 corresponds to the first driving portion 131 inFIG. 1, and the light guiding device 20 corresponds to the first panelportion 111 in FIG. 1. In addition, the second display device 100B shownin FIG. 1 has the same structure as the first display device 100A exceptthat the left and right are reversed, such that the detailed descriptionof the second display device 100B will not be repeated.

The image forming device 10 includes an image display device 11 and aprojective optical system 12. The image display device 11 includes anillumination device 31 that emits two-dimensional illumination light SL,a liquid crystal display device 32 that is a transmission-type spatialoptical modulation device, and a driving control unit 34 that controlsan operation of the illumination device 31 and the liquid crystaldisplay device 32.

The illumination device 31 includes a light source 31 a that generateslight including three colors of red, green, and blue, and a backlightlight-guiding portion 31 b that diffuses the light from the light source31 a and converts this light into a light beam having a rectangularcross-section. The liquid crystal display device 32 spatially modulatesillumination light SL emitted from the illumination device 31 and formsimage light, which is an object to be displayed, such as a movingpicture. The driving control unit 34 includes a light source drivingcircuit 34 a and a liquid crystal driving circuit 34 b. The light sourcedriving circuit 34 a supplies a power to the light source 31 a of theillumination device 31 and allows the illumination light SL with astable brightness to be emitted. The liquid crystal driving circuit 34 boutputs an image signal or a driving signal to the liquid crystaldisplay device 32, and forms colored-image light that becomes an originof the moving picture or a still image as a transmittance pattern. Inaddition, the liquid crystal driving circuit 34 b may be provided withan image processing function, but the image processing function may beprovided to a control circuit that is externally provided. Theprojective optical system 12 is a collimated lens that converts imagelight emitted from each point on the liquid crystal display device 32into a parallel light beam.

In the liquid crystal display device 32, a first direction D1corresponds to an extension direction of a vertical cross-sectionincluding a first optical axis AX1 passing through the projectiveoptical system 12 and a specific line parallel with a third reflectivesurface 21 c of the light guiding member 21, which is described later,and a second direction D2 corresponds to an extension direction of ahorizontal cross-section including the first optical axis AX1 and anormal line of the third reflective surface 21 c. In other words, thefirst direction D1 is a direction parallel with an intersection line CLbetween a first reflective surface 21 a of the light guiding member 21,which is described later, and the third reflective surface 21 c, and thesecond direction D2 is a direction parallel with a plane of the firstreflective surface 21 a and is orthogonal to the intersection line CLbetween the first reflective surface 21 a and the third reflectivesurface 21 c. That is, in regard to a position of the liquid crystaldisplay device 32, the first direction D1 corresponds to a verticalY-direction and the second direction D2 corresponds to a horizontalX-direction.

In addition, in regard to an effective size, the liquid crystal displaydevice 32 has a horizontally long shape, that is, a length in the seconddirection D2 is larger than a length in the first direction D1. On theother hand, an emission opening of the projective optical system 12 hasa vertically long shape, that is, a width in the first direction D1 islarger than a width in the second direction D2.

The light guiding device 20 is formed by bonding the light guidingmember 21 and a light transmitting member 23, and makes up an opticalmember having a flat plate shape that extends in parallel with an XYplane, as a whole.

In the light guiding device 20, the light guiding member 21 is atrapezoidal prism-shaped member in a plan view, has a first reflectivesurface 21 a, a second reflective surface 21 b, a third reflectivesurface 21 c, and a fourth reflective surface 21 d as a side surface. Inaddition, the light guiding member 21 has a top surface 21 e and abottom surface 21 f that are adjacent to the first, second, third, andfourth reflective surfaces 21 a, 21 b, 21 c, and 21 d, and are oppositeto each other. Here, the first and second reflective surfaces 21 a and21 b extend along the XY plane and are separated from each other by athickness t of the light guiding member 21. In addition, the thirdreflective surface 21 c is inclined at an acute angle α of 45° or lesswith respect to the XY plane, and the fourth reflective surface 21 d isinclined, for example, at an acute angle β of 45° or less with respectto the XY plane. The first optical axis AX1 passing through the thirdreflective surface 21 c and a second optical axis AX2 passing throughthe fourth reflective surface 21 d are disposed in parallel with eachother and are separated from each other by a distance D. In addition, aswill be described later in detail, a corner is removed and thereby anend surface 21 h is formed between the first reflective surface 21 a andthe third reflective surface 21 c. When including this end surface 21 h,the light guiding member 21 has an external form of a polyhedral shapewith seven faces,

The light guiding member 21 performs the light guiding using a totalreflection by the first and second reflective surfaces 21 a and 21 b.There are two directions, that is, a direction that is turned back bythe reflection at the time of light-guiding, and a direction that is notturned back by the reflection at the time of light-guiding. When it isconsidered in relation to an image guided by the light guiding member21, a horizontal direction that is turned-back by plural times ofreflection at the time of light-guiding, that is, a confinementdirection corresponds to the second direction D2 of the liquid crystaldisplay device 32 when an optical path is developed to the light sourceside in vertical to the first and second reflective surfaces 21 a and 21b (in parallel with the Z-axis) as described later, a vertical directionthat is not turned-back by the reflection at the time of light-guiding,that is, a free propagation direction corresponds to the first directionD1 of the liquid crystal display device 32 when an optical path isdeveloped to the light source side in parallel with the first and secondreflective surfaces 21 a and 21 b, and the third reflective surface 21 c(in parallel with the Y-axis) as described later.

The light guiding member 21 is formed of a resin material showing a highlight transmitting property at a visible range. The light guiding member21 is a member of a block state, which is integrally molded by aninjection molding, and is formed, for example, by injecting a thermalpolymerization-type resin material into a metal mold and by thermallycuring this molded resin material. In this way, the light guiding member21 is an integrally formed product, but functionally, may be consideredas being classified into a light incidence portion B1, a light guidingportion B2, and a light emission portion B3.

The light incidence portion B1 is a triangular prism-shaped portion andhas a light incidence surface IS that is a part of the first reflectivesurface 21 a, and the third reflective surface 21 c opposite to thelight incidence surface IS. The light incidence surface IS is arear-side or observer-side plane for taking in image light GL from theimage forming device 10, and extends in a direction orthogonal to thefirst optical axis AX1 and opposite to the projective optical system 12.The third reflective surface 21 c is a rectangular total reflectionmirror that reflects the image light GL passed through the lightincidence surface IS and guides this reflected image light GL into thelight guiding portion B2.

FIG. 3A is a diagram illustrating the third reflective surface 21 c, andis a partially enlarged cross-sectional view of a surface portion P1 inthe light incidence portion B1. The third reflective surface 21 c has amirror layer 25 and is coated with a protective layer 26. This mirrorlayer 25 is a total reflection coating and is formed by forming a filmthrough a vapor deposition of aluminum or the like on an inclinedsurface RS of the light guiding member 21. The third reflective surface21 c is inclined with respect to the first optical axis AX1 of theprojective optical system 12 or the XY plane, for example, at an acuteangle α of 25° to 27°, and turns-back the image light GL that isincident from the light incidence surface IS and faces a positiveZ-direction as a whole, in order for the image light GL to face anegative X-direction close to a negative Z-direction as a whole, suchthat the image light GL may be reliably guided into the light guidingportion B2.

Returning to FIG. 2A, the light guiding portion B2 has the firstreflective surface 21 a and the second reflective surface 21 b, whichtotally reflect the image light turned-back by the light incidenceportion B1, as two planes that extend in parallel with the XY plane andopposite to each other. A distance between the first and secondreflective surfaces 21 a and 21 b, that is, a thickness t of the lightguiding member 21 is set to, for example, substantially 9 mm. Here, itis assumed that the first reflective surface 21 a is at a rear side orobserver side that is close to the image forming device 10, and thesecond reflective surface 21 b is at a front side or external side thatis distant from the image forming device 10. In this case, the firstreflective surface 21 a is a plane portion that is common to the lightincidence surface IS described above or a light emission surface OSdescribed later. The first and second reflective surfaces 21 a and 21 bare total reflection surfaces using a difference in refraction indexes,and to which a reflective coat such as a mirror layer is not provided.

FIG. 3B is a diagram illustrating the first reflective surface 21 a, andis a partially enlarged cross-sectional view of a surface portion P1 inthe light guiding portion B2 of the light guiding member 21. Inaddition, FIG. 3C is a diagram illustrating the first reflective surface21 a, and is a partially enlarged cross-sectional view of the surfaceportion P1 in the light guiding portion B2 of the light guiding member21. The first and second reflective surfaces 21 a and 21 b are coatedwith a hard coat layer 27 to prevent damage to a surface and thereby toprevent deterioration in the resolution of a video. This hard coat layer27 is formed by forming a film through a dipping process or a spraycoating process of an UV-curable resin, a thermosetting resin, or thelike on a flat surface FS of the light guiding member 21. The imagelight GL reflected by the third reflective surface 21 c of the lightincidence portion B1 is, first, incident to the first reflective surface21 a and is totally reflected. Next, the image light GL is incident tothe second reflective surface 21 b and is totally reflected.Hereinafter, these operations are repeated, and thereby the image lightis guided to an internal side of the light guiding device 20, that is, anegative X side in which the light emission portion B3 is provided. Inaddition, a reflective coat is not provided to the first and secondreflective surfaces 21 a and 21 b, such that external light that isincident to the second reflective surface 21 b from the external sidepasses through the light guiding portion B2 with a high transmittance.That is, the light guiding portion B2 is formed of a see-through type inwhich the see-through of an external image is possible.

The above-described total reflection at the first and second reflectivesurfaces 21 a and 21 b may be made to occur at an inner side of asurface SS of the hard coat layer 27 through a setting of a refractiveindex of the hard coat layer 27, but may be made to occur at an innerside of the flat surface FS.

Returning to FIG. 2A or the like, the light emission portion B3 is atriangular prism-shaped portion, and has a light emission surface OSthat is a part of the first reflective surface 21 a and the fourthreflective surface 21 d that is opposite to the light emission surfaceOS. The light emission surface OS is a rear-side plane that emits theimage light GL to the observer's eye EY, and is formed of a part of thefirst reflective surface 21 a similarly to the light incidence surfaceIS, and extends in a direction orthogonal to the second optical axisAX2. A distance D between the second optical axis AX2 passing throughthe light emission portion B3 and the first optical axis AX1 passingthrough the light incidence portion B1 is set to, for example, 50 mm inconsideration of the width of the observer's head, or the like. Thefourth reflective surface 21 d is a rectangular flat surface thatreflects the image light GL, which is incident through the first andsecond reflective surfaces 21 a and 21 b, and emits this image light GLto the outside of the light emission portion B3. A half mirror layer 28is provided to be attached to the fourth reflective surface 21 d. Thishalf mirror layer 28 is a reflective film having a light transmittingproperty (that is, a semi-transmissive reflective film), and a surfacethereof serves as a semi-transmissive reflective surface. The halfmirror layer (light-transmitting reflective film or semi-transmissivereflective film) 28 is formed by forming a metallic reflective film or adielectric multi-layer film on the inclined surface RS of the lightguiding member 21. A reflectance of the half mirror layer 28 withrespect to the image light GL is set to 10% to 50% within an assumedangle of incidence range of the image light GL, from an aspect of makingthe observation of external light GL′ easy via a see-through. Thereflectance of the half mirror layer 28 with respect to the image lightGL in a specific example is set to, for example, 20%, and thetransmittance with respect to the image light GL is set to, for example,80%.

FIG. 3D shows a diagram illustrating a structure of the fourthreflective surface 21 d and the periphery thereof, and which isaccompanied by an enlarged diagram of a cross-section of the half mirrorlayer (light-transmitting reflective film or semi-transmissivereflective film) 28. As is clear from the drawing, the half mirror layer(reflective film) 28 includes a metallic reflective film 28 a not havinga polarization characteristic, a first dielectric multi-layer film 28 bhaving the polarization characteristic, and a second dielectricmulti-layer film 28 c having the polarization characteristic. Here, themetallic reflective film 28 a is interposed between the first dielectricmulti-layer film 28 b and the second dielectric multi-layer film 28 c.That is, the half mirror layer 28 has a sandwich structure in which themetallic reflective film 28 a is disposed at the center. The metallicreflective film 28 a is formed of, for example, Ag film, Al film, or thelike. In a case where the metallic reflective film 28 a is formed of theAg film, absorption is small, and a loss caused by the half mirror layer28 is suppressed, such that efficiency may be increased. In addition,the Ag film has lower sensitivity of transmittance with respect anincrease or a decrease in a film thickness compared to the case of theAl film or the like, such that it is easy to adjust the reflectance orthe transmittance of the half mirror layer 28. The lower-side firstdielectric multi-layer film 28 b or the upper-side second dielectricmulti-layer film 28 c is formed by laminating several layers or more oftransparent dielectric layers. That is, both the dielectric multi-layerfilms 28 b and 28 c are formed by laminating materials of plural kindsof refraction indexes through a vapor deposition, and are made to havean angle of incidence dependency with respect to the reflectance or thetransmittance through an interference action. As a high refraction indexmaterial making up these dielectric multi-layer films 28 b and 28 c, forexample, a light transmitting material such as SiO₂ and MgF may beexemplified. In addition, as a middle refraction index material makingup these dielectric multi-layer films 28 b and 28 c, a lighttransmitting material such as TiO₂, Ta₂O₅, and ZrO₂ may be exemplified.As a low refraction index material making up these dielectricmulti-layer films 28 b and 28 c, a light transmitting material such asAl₂O₃ may be exemplified.

FIG. 4 shows a graph illustrating a reflectance characteristic of thehalf mirror layer (reflective film) 28. Here, the horizontal axisrepresents an angle of incidence of light to the half mirror layer 28and the vertical axis represents a reflectance. FIG. 5 shows a graphillustrating a wavelength dependency of a reflectance of light beamsthat are incident to the half mirror layer 28 at angle of 25° to 70°.Here, the horizontal axis represents a wavelength of light that isincident to the half mirror layer 28 and the vertical axis represents areflectance. In FIG. 5, a reflectance at the angle of incidence of 25°is indicated by a dotted line, and a reflectance at the angle ofincidence of 70° is indicated by a solid line.

As is clear from the above-described graphs, light that is incident tothe half mirror layer 28 at an angle of incidence that is equal to orless than a reference angle or a lower limit angle set to substantially40° is reflected with a reflectance of substantially 20%, and light thatis incident to the half mirror layer 28 at an angle of incidence that islarger than the lower limit angle is reflected with a reflectance thatincreases drastically from 20% accompanying the increase in the angle ofincidence, and is almost reflected with a reflectance of substantially100% at an angle of 50° or more. Here, the lower limit angle correspondsto the upper limit of an angle of incidence range of 10° to 40° that isassumed in relation to the image light GL that is incident to the halfmirror layer 28, and prevents light beams with a large angle ofincidence other than the image light GL, specifically, ghost light frombeing incident to the eye EY. It will be described later in detail withrespect to the removing of the ghost light, but the angle of incidenceat the rear side of the half mirror layer 28 is generally set to 60° ormore.

In addition, a reflectance of the half mirror layer 28 with respect tothe image light GL that is incident to the half mirror layer 28 at anangle that is equal to or less than the lower limit angle is not limitedto 20% and may be appropriately changed according to use. In addition,in relation to the reflectance of the half mirror layer 28 with respectto the image light GL that is incident to the half mirror layer 28 at anangle that is equal to or less than the lower limit angle, it ispreferable that dependency with respect to an angle or a wavelength besmall, and strictly, it is not necessary to be uniform.

Returning to FIG. 2B or the like, the fourth reflective surface 21 d isinclined, for example, at an acute angle α of 25° to 27° with respect tothe second optical axis AX2 or XY plane that is orthogonal to the firstreflective surface 21 a, and the image light GL, which is incidentthrough the first and second reflective surfaces 21 a and 21 b of thelight guiding portion B2, is partially reflected by the half mirrorlayer 28 and is made to turn back to face the negative Z-direction as awhole, and thereby the image light GL passes through the light emissionsurface OS. In addition, the image light GL that is transmitted throughthe fourth reflective surface 21 d is incident to the light transmittingmember 23 and is not used for forming a video.

The light transmitting member 23 has the same refractive index as a mainbody of the light guiding member 21, and has a first surface 23 a, asecond surface 23 b, and a third surface 23 c. The first and secondsurfaces 23 a and 23 b extend along the XY plane. In addition, the thirdsurface 23 c is inclined with respect to the XY plane, and is disposedto be opposite to the fourth reflective surface 21 d of the lightguiding member 21 and in parallel therewith. That is, the lighttransmitting member 23 is a member having a wedge-shaped portion that isinterposed between the second surface 23 b and the third surface 23 c.The light transmitting member 23 is formed of a resin material showing ahigh light transmitting property at a visible range similarly to thelight guiding member 21. The light transmitting member 23 is a member ofa block state, which is integrally molded by an injection molding, andis formed, for example, by injecting a thermal polymerization-type resinmaterial into a metal mold and by thermally curing this molded resinmaterial.

In the light transmitting member 23, the first surface 23 a is disposedon an extended plane of the first reflective surface 21 a provided tothe light guiding member 21 and is located at a rear side close to theobserver's eye EY, and the second surface 23 b is disposed on anextended plane of the second reflective surface 21 b provided to thelight guiding member 21 and is located at a front side distant from theobserver's eye EY. The third surface 23 c is a rectangular transmissivesurface that is bonded to the fourth reflective surface 21 d of thelight guiding member 21 by an adhesive. An angle made by the firstsurface 23 a and the third surface 23 c is the same as an angle ε madeby the second reflective surface 21 b and the fourth reflective surface21 d of the light guiding member 21, and an angle made by the secondsurface 23 b and the third surface 23 c is the same as an angle β madeby the first reflective surface 21 a and the third reflective surface 21c of the light guiding member 21.

The light transmitting member 23 and the light guiding member 21 make upa see-through portion B4 corresponding to a portion opposite to theobserver's eye at a bonding portion of these members and in the vicinityof the bonding portion. A wedge-shaped member 23 m, which is interposedbetween the second surface 23 b and the third surface 23 c making anacute angel in the light transmitting member 23 and extends in thenegative X-direction, is bonded to the wedge-shaped light emissionportion B3 and thereby makes up a central portion in the X-direction inthe plate-shaped see-through portion B4. A reflective coat such as amirror layer is not provided to the first and second surfaces 23 a and23 b, such that these surfaces transmit the external light GL′ with ahigh transmittance similarly to the light guiding portion B2 of thelight guiding member 21. The third surface 23 c may also transmits theexternal light GL′ with a high transmittance, but the fourth reflectivesurface 21 d of the light guiding member 21 is provided with the halfmirror layer 28, such that the external light GL′ after passing throughthe third surface 23 c is reduced, for example, by 20%. That is, anobserver observes light in which the image light GL reduced to 20% andthe external light GL′ reduced to 80% overlap with each other.

C. Outline of Optical Path of Image Light

FIG. 6A shows a diagram illustrating an optical path in the firstdirection D1 corresponding to a vertical cross-section CS1 of the liquidcrystal display device 32. In the vertical cross-section along the firstdirection D1, that is, a YZ plane (a Y′Z′ plane after being developed),in the image light emitted from the liquid crystal display device 32, acomponent, which is emitted from an upper end side (a positive Y side)of a display region 32 b, indicated by a one-dotted line in the drawingis set as image light GLa, and a component, which is emitted from alower end side (a negative Y side) of a display region 32 b, indicatedby a two-dotted line in the drawing is set as image light GLb.

The upper-side image light GLa is converted into a parallel light beamby the projective optical system 12, passes through the light incidenceportion B1, the light guiding portion B2, and the light emission portionB3 of the light guiding member 21 along the developed optical axis AX′,and is incident to the observer's eye EY from an upper-side directioninclined at an angle of φ₁, in a parallel light beam state with respectto the observer's eye EY. On the other hand, the lower-side image lightGLb is converted into a parallel light beam by the projective opticalsystem 12, passes through the light incidence portion B1, the lightguiding portion B2, and the light emission portion B3 of the lightguiding member 21 along the developed optical axis AX′, and is incidentto the observer's eye EY from a lower side direction inclined at anangle of φ₂ (|φ₂|=|φ₁|) in a parallel light beam state with respect tothe observer's eye EY. The angles φ₁ and φ₂ correspond to an upper halfangle of view and a lower half angle of view, respectively, and are setto, for example, 6.5°.

FIG. 6B shows a diagram illustrating an optical path in the seconddirection (confinement direction or composite direction) D2corresponding to a horizontal cross-section CS2 of the liquid crystaldisplay device 32. In the horizontal cross-section along the seconddirection (confinement direction or composite direction) D2, that is, aXZ plane (a X′Z′ plane after being developed), in the image lightemitted from the liquid crystal display device 32, a component, which isemitted from a first display point P1 of a right end side (a positive Xside) toward the display region 32 b, indicated by a one-dotted line inthe drawing is set as image light GLc, and a component, which is emittedfrom a second display point P2 of a left end side (a negative X side)toward the display region 32 b, indicated by a two-dotted line in thedrawing is set as image light GLd. In FIG. 6B, image light GLe emittedfrom a right inner side and image light GLf emitted from a left innerside are added for reference.

The image light GLc from the right-side first display point P1 isconverted into a parallel light beam by the projective optical system12, passes through the light incidence portion B1, the light guidingportion B2, and the light emission portion B3 of the light guidingmember 21 along the developed optical axis AX′, and is incident to theobserver's eye EY from a right side direction inclined at an angle ofθ₁, in a parallel light beam state with respect to the observer's eyeEY. On the other hand, the image light GLd from the left-side seconddisplay point P2 is converted into a parallel light beam by theprojective optical system 12, passes through the light incidence portionB1, the light guiding portion B2, and the light emission portion B3 ofthe light guiding member 21 along the developed optical axis AX′, and isincident to the observer's eye EY from a left-side direction inclined atan angle of θ₂ (|θ₂|=|θ₁|) in a parallel light beam state with respectto the observer's eye EY. The angles θ₁ and θ₂ correspond to a left halfangle of view and a right half angle of view, respectively, and are setto, for example, 10°.

In addition, in regard to the horizontal direction, that is, the seconddirection D2, the image light beams GLc and GLd are turned back byreflection inside the light guiding member 21 and the number of times ofreflection of the image light beams GLe and GLd is different in eachcase, such that each of the image light beams GLc and GLd isdiscontinuously expressed in the light guiding member 21. In addition,in regard to the observer's eye EY, a viewing direction is verticallyinverted compared to the case of FIG. 2A. Consequently, in regard to thehorizontal direction, a screen is horizontally inverted as a whole, butas described later in detail, when the light guiding member 21 isprocessed with high accuracy, a right half image of the liquid crystaldisplay device 32 and a left half image of the liquid crystal displaydevice 32 are continuously combined without deviation. In addition, inconsideration of the difference in the number of times of reflection ofthe image light beams GLc and GLd inside the light guiding member 21,the angle of emission θ₁′ of the right-side image light GLc and theangle of emission θ₂′ of the left-side image light GLd are made to bedifferent from each other.

As described above, the image light beams GLa, GLb, GLc, and GLd thatare incident to the observer's eye EY become virtual images frominfinite distance, such that in regard to the first vertical directionD1, a video formed on the liquid crystal display device 32 is erected,and in regard to the second horizontal direction D2, a video formed onthe liquid crystal display device 32 is inversed.

D. Optical Path of Image Light in Relation to Horizontal Direction

FIG. 7 shows a cross-sectional view illustrating a specific optical pathin the first display device 100A. The projective optical system 12includes three lenses L1, L2, and L3.

When passing through the lenses L1, L2, and L3 of the projective opticalsystem 12, image light beams GL11 and GL12 from the right-side firstdisplay point P1 of the liquid crystal display device 32 are convertedinto parallel light beams, and are incident to the light incidencesurface IS of the light guiding member 21. The image light beams GL11and GL12 guided to the inside of the light guiding member 21 repeat atotal reflection on the first and second reflective surfaces 21 a and 21b at the same angle, and are eventually emitted from the light emissionsurface OS as a parallel light beam. Specifically, the image light beamsGL11 and GL12 are reflected by the third reflective surface 21 c of thelight guiding member 21 as a parallel light beam, and then are incidentto the first reflective surface 21 a of the light guiding member 21 at afirst reflection angle γ1 and are totally reflected (total reflection ofa first time). Then, the image light beams GL11 and GL12 are incident tothe second reflective surface 21 b while maintaining the firstreflection angle γ1 and are totally reflected (total reflection of asecond time), and then are incident to the first reflective surface 21 aagain and are totally reflected (total reflection of a third time). As aresult, the image light beams GL11 and GL12 repeat the total reflectionon the first and second reflective surfaces 21 a and 21 b whilemaintaining the first reflection angle γ1. The image light beams GL11and GL12 are totally reflected by the first and second reflectivesurfaces 21 a and 21 b three times in total, and are incident to thefourth reflective surface 21 d. The image light beams GL11 and GL12 arereflected by the fourth reflective surface 21 d at the same angle as thethird reflective surface 21 c and are emitted from the light emissionsurface OS as a parallel light beam at an inclination of an angle θ₁with respect to the second optical axis AX2 direction that is orthogonalto the light emission surface OS.

When passing through the lenses L1, L2, and L3 of the projective opticalsystem 12, image light beams GL21 and GL22 from the left-side seconddisplay point P2 of the liquid crystal display device 32 are convertedinto parallel light beams, and are incident to the light incidencesurface IS of the light guiding member 21. The image light beams GL21and GL22 guided to the inside of the light guiding member 21 repeat atotal reflection on the first and second reflective surfaces 21 a and 21b at the same angle, and are eventually emitted from the light emissionsurface OS as a parallel light beam. Specifically, the image light beamsGL21 and GL22 are reflected by the third reflective surface 21 c of thelight guiding member 21 as a parallel light beam, and then are incidentto the first reflective surface 21 a of the light guiding member 21 at asecond reflection angle γ2 (γ2<γ1) and are totally reflected (totalreflection of a first time). Then, the image light beams GL21 and GL22are incident to the second reflective surface 21 b while maintaining thesecond reflection angle γ2 and are totally reflected (total reflectionof a second time), are incident again to the first reflective surface 21a and are totally reflected (total reflection of a third time), areincident again to the second reflective surface 21 b and are totallyreflected (total reflection of a fourth time), and are incident again tothe first reflective surface 21 a and are totally reflected (totalreflection of a fifth time). As a result, the image light beams GL21 andGL22 are totally reflected by the first and second reflective surfaces21 a and 21 b five times in total and are incident to the fourthreflective surface 21 d. The image light beams GL21 and GL22 arereflected by the fourth reflective surface 21 d at the same angle as thethird reflective surface 21 c and are emitted from the light emissionsurface OS as a parallel light beam at an inclination of an angle θ₂with respect to the second optical axis AX2 direction that is orthogonalto the light emission surface OS.

In FIG. 7, a first virtual surface 121 a corresponding to the firstreflective surface 21 a in a case where the light guiding member 21 isdeveloped, and a second virtual surface 121 b corresponding to thesecond reflective surface 21 b in a case where the light guiding member21 is developed are illustrated. Through such a development, it can beseen that the image light beams GL11 and GL12 from the first displaypoint P1 pass through an incident equivalent surface IS′ correspondingto the light incidence surface IS, pass through the first surface 121 atwo times, pass through the second surface 121 b one times, are emittedfrom the light emission surface OS, and are incident to the observer'seye EY. In addition, it can be seen that the image light beams GL21 andGL22 from the second display point P2 pass through an incidenceequivalent surface IS″ corresponding to the light incidence surface IS,pass through the first surface 121 a three times, pass through thesecond surface 121 b two times, are emitted from the light emissionsurface OS, and are incident to the observer's eye EY. In other words,the observer observes the lens L3 of the projective optical system 12that is present in the vicinity of the two incidence equivalent surfacesIS′ and IS″ that are present at positions different from each other inan overlapped manner.

FIG. 8A shows a diagram illustrating a conception of a display surfaceof a liquid crystal display device 32, FIG. 8B is a diagram illustratinga conception of a virtual image of the liquid crystal display device 32,which is viewed to an observer, and FIGS. 8C and 8D are diagramsillustrating partial images making up the virtual image. A rectangularimage forming region AD provided to the liquid crystal display device 32shown in FIG. 8A is observed as a virtual image display region AI shownin FIG. 8B. A first projection image IM1 corresponding to a portionranging from center to right-side in the image forming region AD of theliquid crystal display device 32 is formed at a left-side of the virtualimage display region AI, and this first projection image IM1 becomes apartial image in which a right-side is deficient as shown in FIG. 8C. Inaddition, a second projection image IM2 corresponding to a portionranging from center to left-side in the image forming region AD of theliquid crystal display device 32 is formed as a virtual image at a rightside of the virtual image display region AI, and this second projectionimage IM2 becomes a partial image in which a left half is deficient asshown in FIG. 8D.

A first partial region A10, which forms only the first projection image(virtual image) IM1 in the liquid crystal display device 32 shown inFIG. 8A, includes, for example, the first display point P1 of the rightend of the liquid crystal display device 32 and emits the image lightbeams GL11 and GL12 that are totally reflected in the light guidingportion B2 of the light guiding member 21 three times in total. A secondpartial region A20, which forms only the second projection image(virtual image) IM2 in the liquid crystal display device 32, includes,for example, the second display point P2 of the left end of the liquidcrystal display device 32 and emits the image light beams GL21 and GL22that are totally reflected in the light guiding portion B2 of the lightguiding member 21 five times in total. Image light from a band SA nearthe center of the image forming region AD of the liquid crystal displaydevice 32, which is interposed between the first and second partialregions A10 and A20 and extends vertically, forms a superimposed imageSI shown in FIG. 8B. That is, image light from the band SA of the liquidcrystal display device 32 includes the first projection image IM1 formedby the image light beams GL11 and GL12 that are totally reflected in thelight guiding portion B2 three times in total, and the second projectionimage IM2 formed by the image light beams GL21 and GL22 that are totallyreflected in the light guiding portion B2 five times in total, and thesefirst and second projection image IM1 and IM2 overlap with each other onthe virtual image display region AI. When the light guiding member 21 isaccurately processed, and thereby a light beam that is accuratelycollimated by the projective optical system 12 is formed, it is possibleto prevent deviation or bleeding due to overlapping of the twoprojection images IM1 and IM2 with respect to the superimposed image IS.In addition, a horizontal width or an overlapping width of the band SAwhere the overlapping occurs may be adjusted by controlling an anglerange of the illumination light SL that illuminates the liquid crystaldisplay device 32. In this embodiment, the angle range of theillumination light SL is not particularly adjusted, such that the bandSA of the horizontal width or the overlapping width that corresponds toa divergence characteristic of the backlight light-guiding portion 31 bor the like is present.

Hereinbefore, the number of times of total reflection of the image lightbeams GL11 and GL12 emitted from the first partial region A10 includingthe first display point P1 of the right-side of the liquid crystaldisplay device 32 by the first and second reflective surfaces 21 a and21 b is set to three times in total, and the number of times of totalreflection of the image light beams GL21 and 22 emitted from the secondpartial region A20 including the second display point P2 of theleft-side of the liquid crystal display device 32 by the first andsecond reflective surfaces 21 a and 21 b is set to five times in total,but the number of times of total reflection may be appropriatelychanged. That is, through an adjustment of external form (that is, thethickness t, the distance D, and acute angles α and β) of the lightguiding member 21, the number of times of total reflection of the imagelight beams GL11 and GL12 may be set to five times in total, and thenumber of times of total reflection of the image light beams GL21 andGL22 may be set to seven times in total. In addition, hereinbefore, thenumber of times of total reflection of the image light beams GL11, GL12,GL21, and GL22 is an odd number, but when the light incidence surface ISand the light emission surface OS are disposed at an opposite side, thatis, the light guiding member 21 is made to have a parallelogram shape ina plan view, the number of times of total reflection of the image lightbeams GL11, GL12, GL21, and GL22 becomes an even number.

E. Processing of Ghost Light

FIG. 9 shows an enlarged diagram illustrating a processing of ghostlight in a light guiding device 20. In regard to the light emissionportion B3 of the light guiding member 21, the image light GL that isincident after passing through the first and second reflective surfaces21 a and 21 b is reflected by the fourth reflective surface 21 d andpasses through the light emission surface OS. At this time, the fourthreflective surface 21 d serves as a half mirror, such that the imagelight GL passes through the fourth reflective surface 21 d withintensity of, for example, substantially 80% and may become ghost lightGG. That is, the image light GL passed through the fourth reflectivesurface 21 d is reflected by the second surface 23 b, but in a casewhere this image light GL passes through the fourth reflective surface21 d, this image light GL may pass through the first reflective surface21 a or the fourth reflective surface 21 d and thereby may become theghost light GG that is relatively conspicuous. In this embodiment, thisghost light GG is blocked by a half mirror layer (light-transmittingreflective film or semi-transmissive reflective film) 28 having an anglecharacteristic.

In addition, the ghost light GG caused by the image light GL that passesthrough the fourth reflective surface 21 d may occur because it is noteasy to form the second surface 23 b to be strictly parallel withrespect to the second reflective surface 21 b due to bonding accuracy orthe like, or the like. More specifically, the second reflective surface21 b of the light guiding member 21 and the second surface 23 b of thelight transmitting member 23 are disposed to be substantially flush witheach other, but strictly, these are not disposed to be flush with eachother. That is, in a case where it is tried to dispose the secondreflective surface 21 a and the second surface 23 b to be strictly flushwith each other, the cost increases extremely. On the other hand, whenthe second reflective surface 21 a and the second surface 23 b aredisposed to be substantially flush with each other, it is not difficultto observe the outside through the see-through portion B4. Therefore, inrelation to a parallelism between the second reflective surface 21 a ofthe light guiding member 21 and the second surface 23 b of the lighttransmitting member 23, it is preferable that stringency be mitigated topromote the easiness of production or the cost reduction. However,according to a review by the present inventors, they found that evenwhen the second surface 23 b of the light transmitting member 23 isinclined at a minuscule angle (for example, several minutes of arc) withrespect to the second reflective surface 21 a of the light guidingmember 21, the ghost light GG may be observed to the eye EY. That is,there is no problem when the second reflective surface 21 a and thesecond surface 23 b are strictly parallel with each other, but when thesecond reflective surface 21 a and the second surface 23 b make theminuscule angle, there is a concern that unnecessary light HL, whichpasses through the fourth reflective surface 21 d, is reflected by thesecond surface 23 b, and passes again through the fourth reflectivesurface 21 d, may pass through the light emission portion B3 at the sameangle condition as the image light GL and may be incident to the eye EY.This unnecessary light HL is not strictly parallel with the image lightGL due to the minuscule angle made by the second reflective surface 21aand the second surface 23 b, and has a slight angle deviation withrespect to the image light GL. Therefore, the unnecessary light HL maybe observed as the ghost light GG, that is, a bleeding with respect tothe image light GL or a double image. Hereinbefore, a case where thesecond surface 23 b makes a minuscule angle with respect to the secondreflective surface 21 a is described, but processing accuracy itself ofthe light transmitting member 23 may have such an effect. That is, thelight transmitting member 23 is acceptable as long as the see-through isexcellent, and originally, substantially the same processing accuracy asthe light guiding member 21 is not required. However, when the flatnessof the second surface 23 b is low, because of the same reason as theabove there is a concern that the unnecessary light HL, which isreflected by the second surface 23 b in which the flatness is low, andpasses again through the fourth reflective surface 21 d, may be observedas the ghost light GG.

To block such ghost light GG, it is preferable to decrease atransmittance of the ghost light GG at the fourth reflective surface 21d. Here, an angle of incidence ζ of the image light GL to the fourthreflective surface 21 d may be set to an angle of incidence range 10° to40° according to a design condition of external form of the lightguiding member 21 as described above, such that the upper limit of theangle of incidence ζ may be set to substantially 40° that is equal to orlarger than the lower limit angle of reflection at the half mirror layer28. On the other hand, an angle of incidence η of the ghost light GG tothe fourth reflective surface 21 d is 60° or more according to theabove-described design condition of the external form of the lightguiding member 21. Therefore, when angle dependency of the reflectanceof the fourth reflective surface 21 d is adjusted as shown in FIG. 4,the transmittance of the ghost light GG at the fourth reflective surface21 d decreases greatly, and thereby it is possible to block theincidence to the eye EY, and the image light GL is appropriatelyreflected to the light emission surface OS side. Accordingly, it ispossible to prevent the observation of the virtual image from beinghindered.

In addition, in relation to the external light, in a case where theexternal light has the same angle condition as the ghost light GG, theexternal light may be perfectly reflected by the fourth reflectivesurface 21 d and may not be incident to the eye EY, but the externallight blocked in this manner is external light from a considerablyinclined direction, and there is no problem in practical use.

F. The Others

FIG. 10A shows a diagram illustrating a modification of the lightguiding member 21 shown in FIG. 2A and the like. In the abovedescription, it is described that the image light that is propagated bythe light guiding member 21 is totally reflected with respect to thefirst and second reflective surfaces 21 a and 21 b at two reflectionangles γ1 and γ2, but similarly to the light guiding member 21 of themodification shown in FIG. 10A, three components of image light GL31,GL32, and GL33 may be permitted to be totally reflected at reflectionangles γ1, γ2, and γ3 (γ1>γ2>γ3), respectively. In this case, the imagelight GL emitted from the liquid crystal display device 32 is propagatedin three modes, and is combined at a position of the observer's eye EYand becomes a virtual image. In this case, as shown in FIG. 10B, aprojection image IM21 subjected to the total reflection, for example,three times in total is formed at a left-side of the effective displayregion A0, a projection image IM22 subjected to the total reflection,for example, five times in total is formed near the center of theeffective display region A0, and a projection image IM23 subjected tothe total reflection, for example, seven times in total is formed at aright-side of the effective display region A0.

FIG. 11 shows an enlarged diagram illustrating the reason why an endsurface 21 h formed by removing a corner is provided to the lightguiding member 21 shown in FIG. 2A or the like. The image light GLincident to a position near a corner 121 h of the light guiding member21 is reflected by the third reflective surface 21 c and then isreflected by the first reflective surface 21 a, but the image light GLis reflected by the first reflective surface 21 a and then is reflectedagain by the third reflective surface 21 c. The unnecessary light HL assuch re-reflected light is not parallel with the original image light GLdue to the reflection at the third reflective surface 21 c and is guidedto an unforeseen optical path, and thereby a part thereof may be guidedto the light emission portion B3 and may be emitted from the lightemission surface OS. That is, the unnecessary light HL generated at thecorner 121 h becomes the ghost light GG that is not preferable as shownin FIG. 9, such that it is preferable to remove the unnecessary light HLin advance. Therefore, the corner 121 h is removed to provide an endsurface 21 h that blocks stray light and thereby imposes restrictions onthe optical path of the unnecessary light HL.

FIG. 12 shows an enlarged diagram illustrating a modification of thelight guiding member 21 shown in FIG. 2A or the like. In this case, anend surface 21 i, which is formed by removing a corner 121 i, isprovided to the fourth reflective surface 21 d side of the light guidingmember 21. That is, the light guiding member 21 has an external form ofa polyhedral shape with eight faces. A coat or a roughened surface with,for example, a relatively high reflectance is formed on the end surface21 i, and a step difference that is fitted to the end surface 21 i isalso provided to the light transmitting member 23. By providing such anend surface 21 i, it is possible to prevent the unnecessary light HL,which occurs in a case where the normal image light GL propagatedthrough the light guiding member 21 is reflected by the fourthreflective surface 21 d two times or more, or the unnecessary light HL,which occurs in a case where the normal image light GL passes throughthe light guiding portion B2 by being reflected less than three timesand is reflected by the fourth reflective surface 21 d, from beingemitted to the outside through the light emission surface OS. That is,the end surface 21 i prevents the unnecessary light HL, which isinclined with respect to the original image light GL after passingthrough a path other than an assumed path, from being the ghost light GGthat is not preferable similarly to the case of FIG. 9.

In the above-described virtual image display device 100, the image lightGL reflected by the third reflective surface 21 c of the light incidenceportion B1 is propagated while being totally reflected by the first andsecond reflective surfaces 21 a and 21 b of the light guiding portion,and is reflected by the fourth reflective surface 21 d of the lightemission portion B3, and is incident to the observer's eye EY as avirtual image. At this time, the number of times of reflection of thefirst image light beams GL11 and GL12, which are emitted from the firstpartial region A10 including the first display point P1 of the imagedisplay device 11, at the light guiding portion, and the number of timesof reflection of the second image light beams GL21 and GL22, which areemitted from the second partial region A20 including the second displaypoint P2 of the image display device 11, at the light guiding portionB2, are different from each other, such that it is possible to take awide angle width of an angle of emission of the image light GL emittedfrom the light emission portion B3. That is, it is possible to take inthe image light GL from the different partial regions A10 and A20 in theimage display device 11 at a relatively wide viewing angle, such that itis possible to secure a large display size of a virtual image that isobserved over the light emission portion B3. In this way, it isconfigured to have a structure in which image light beams GL in whichthe number of times of reflection is different are taken out, such thatit is possible to make the light emission portion B3 large so as tocover a pupil without making the light guiding portion B2 too muchthicker, and therefore it is not necessary to perform a pupil divisionby making the light emission portion B3 close to the pupil. As a result,it is possible to secure a large Eyring diameter and thereby preferablesee-through observation may be realized.

In addition, in the virtual image display device 100 of the embodiment,the half mirror layer 28 provided between the light emission portion B3and the light transmitting member 23 as a reflective film has the angledependency in which when the angle of incidence becomes larger than theangle of incidence range of the image light GL, the reflectanceincreases, such that it is possible to prevent unintended light, whichis emitted to the light transmitting member 23 from the light guidingmember 21 and is reflected inside the light transmitting member 23, frombeing returned to the light emission portion B3 of the light guidingmember 21 after passing through the half mirror layer 28 as a reflectivefilm at a relatively large angle of incidence. Therefore, it is possibleto prevent the image light GL passed through the light transmittingmember 23 from becoming ghost light GG while mitigating the demand forincreasing processing accuracy of the light transmitting member 23, andbonding accuracy between the light guiding member 21 and the lighttransmitting member 23, and thereby it is possible to make a virtualimage displayed by a virtual image display device 100 have a highquality.

Hereinbefore, the invention is described based on the embodiment, butthe invention is not limited to the embodiment, and may be executed withvarious aspects without departing from the scope of the invention. Forexample, the following modifications may be made.

In the above-described embodiment, the reflectance of the half mirrorlayer 28 provided on the fourth reflective surface 21 d of the lightguiding member 21 is set to 20% and thereby priority is given to thesee-through, but the reflectance of the half mirror layer 28 is set to50% or more and thereby priority may be given to the image light. Inaddition, the half mirror layer 28 may not be formed on the entirety ofthe fourth reflective surface 21 d, and may be formed at a necessarypartial region. In addition, the half mirror layer 28 may be on thethird surface 23 c of the light transmitting member 23.

A shape of the light transmitting member 23 is not limited to a shapeobtained by extending the light guiding member 21 in the horizontaldirection, that is, in the X-direction, and may include a portion thatis extended to vertically interpose the light guiding member 21.

In the above-described embodiment, the illumination light SL from theillumination device 31 is made not to have a particular directivity, butthe illumination light SL may have a directivity according to a positionof the liquid crystal display device 32. According to thisconfiguration, it is possible to effectively illuminate the liquidcrystal display device 32 and thereby it is possible to reduce avariation in brightness due to a position of the image light GL.

In the above-described embodiment, a display brightness of the liquidcrystal display device 32 is not particularly adjusted, but the displaybrightness may be adjusted according to a range or a superimposition ofthe projection images IM1 and IM2 as shown in FIG. 8B.

In the above-described embodiment, the transmission-type liquid crystaldisplay device 32 or the like is used as the image display device 11,but as the image display device 11, various devices may be used withoutbeing limited to the transmission-type liquid crystal display device 32.For example, a configuration using a reflective liquid crystal displaydevice is possible, and a digital micro mirror device or the like may beused instead of the liquid crystal display device 32. In addition, asthe image display device 11, a self-luminescent device represented by anLED array, an OLED (organic EL), or the like may be used.

The virtual image display device 100 of the above-described embodimentis configured to have a pair of image forming device 10 and lightguiding device 20 in correspondence with each of a right eye and a lefteye, but the virtual image display device 100 may be configured to havethe image forming device 10 and the light guiding device 20 to eitherthe right eye or the left eye to view an image with one eye.

In the above-described embodiment, the first optical axis AX1 passingthrough the light incidence surface IS and the second optical axis AX2passing through the light incidence surface IS are parallel with eachother, but these optical axes AX1 and AX2 may be not parallel with eachother.

In the above description, the virtual image display device 100 isspecifically described as a head-mounted display, but the virtual imagedisplay device 100 may be modified as a head-up display.

In the above description, in regard to the first and second reflectivesurfaces 21 a and 21 b, image light is totally reflected by an interfacewith air and is guided without forming a mirror, a half mirror, or thelike on the surface, but the total reflection of the invention includesa reflection that occurs in a state where a mirror coat or a half mirrorfilm is formed on the entirety of the first and second reflectivesurfaces 21 a and 21 b or a part thereof. For example, the totalreflection of the invention includes a case where an angle of incidenceof image light satisfies a total reflection condition, the mirror coator the like is formed on the entirety of the first and second reflectivesurfaces 21 a and 21 b or a part thereof and thereby substantially allof the image light is reflected. In addition, as long as a sufficientlybright image light is obtained, the entirety of the first and secondreflective surfaces 21 a and 21 b or a part thereof may be coated with amore or less transmissive mirror.

In the above description, the light guiding member 21 extends in thehorizontal direction that is parallel with the eye EY, but the lightguiding member 21 may extend in the vertical direction. In this case,the optical panel 110 has a parallel configuration in parallel not inseries.

What is claimed is:
 1. A virtual image display device, comprising: alight guiding member, comprising: a light guiding portion, a lightincidence portion; and a light emission portion; a light transmittingmember that makes up a see-through portion; and a semi-transmissivereflective surface comprising a plurality of layers, in which a metallicreflective film is disposed adjacent to at least one dielectricmultilayer film, the semi-transmissive reflective surface reflecting aplurality of image light beams having the same angle as image lightbeams reflected from another reflective surface, and are emitted from asurface of the light emission portion as parallel light beams at aspecific inclination angle with respect to an optical axis directionthat is orthogonal to the surface of the light emission portion.
 2. Avirtual image display device according to claim 1, the semi-transmissivereflective surface formed of an Ag film and an Al film.